What is the main difference between a primary and general election?

A Primary Election is held by political parties to select their nominees for the offices to be elected at the upcoming General Election. In a primary, Republicans run against Republicans and Democrats run against other Democrats. And, of course, if other parties qualify to appear on the primary ballot, their candidates run against each other as well. During a Primary voters may choose only one party to vote for.

The General Election determines which candidates will occupy the offices that are up for election. In partisan races, candidates that were nominated at the Primary election compete for races along with any candidates without political party affiliation. Nonpartisan races typically appear on the General Election ballot as well, such as judicial, school and library board races.